Fig. 1

Overexpression of Wnt8a or loss of Nkx2.5 causes a shift in endocardial chamber proportions. a–c Reconstruction of confocal z-stacks show the endothelial-specific transgenic reporter lines Tg(kdrl:EGFP)^s843 or Tg(fli1a:nEGFP)^y7 (green), Phalloidin 568-stained Actin (red) and anti-Myh6 labeling of the myocardial atrial chamber (magenta). Compared to (a) WT, (b) overexpression of Wnt8a, or (c) the nkx2.5^vu179 mutation, causes a relative shift of endocardial chamber dimensions. d–f Reconstructions of confocal z-stacks shows that the arterial endothelial transgene Tg(flt1:YFP)^hu4624 marks the ventricular chamber whereas the myocardial atrial marker anti-Myh6 labels the atrial chamber. Compared to (d) WT, (e) overexpression of Wnt8a, or (f) loss of Nkx2.5/Nkx2.7 results in relative shifts of chamber dimensions as indicated by the ventricular-specific expression of Tg(flt1:YFP)^hu4624 within the endocardium. A, atrium; V, ventricle. Scale bars, 30 μm. g Quantifications of endocardial cell numbers in WT (kdrl:GFP n = 11 hearts, fli1a:nEGFP n = 27 hearts), Tg(hsp70l:wnt8a-GFP)^w34 (n = 8 hearts), or nkx2.5^vu179 mutants (n = 27 hearts) reveal that atrial endocardial cell numbers are significantly increased and ventricular endocardial cell numbers are significantly reduced compared to WT. Mean values ± SD are shown. Two-way ANOVA was used to compare each condition with its WT control in each individual chamber (****p < 0.0001)